Reflective optical network architectures seeded with a continuous wave (CW) optical signal have been recognized as a viable solution to deploy wavelength division multiplexed (WDM) Passive Optical Networks (PONs) in which the Optical Network Units (ONUs) are wavelength agnostic (“colourless”). The performance of reflective optical networks is limited by the power budget on the upstream optical path, which is twice as long as the downstream path, and by channel cross-talk induced by lumped or distributed reflections along the fibre link. The main limiting factor in the uplink channel is coherent crosstalk generated by Rayleigh Back-scattering (RB) and by randomly located reflective sites such as fibre connectors and splices. One proposed solution to this problem has been to use reflective modulators which provide optical gain at the ONUs, such as a reflective semiconductor optical amplifier (R-SOA), to keep the uplink crosstalk-to-signal ratio (C/S) at an acceptable value. However, ONU gain cannot be increased arbitrarily: above a threshold it also strongly amplifies the crosstalk. Another proposed solution, reported by P. J. Urban et al, “Mitigation of reflection induced cross-talk in a WDM access network”, OFC 2008, OThT3”, is phase modulation of the CW seed signal. However, the phase modulation must be operated at frequencies outside the data bandwidth, and this likely to be neither a practical nor cheap solution in real systems.